Correlating structure with fluorescence emission in phase-separated conjugated-polymer blends

Abstract

Blends of conjugated polymers are frequently used as the active semiconducting layer in light-emitting diodes and photovoltaic devices. Here we report the use of scanning near-field optical microscopy, scanning force microscopy and nuclear-reaction analysis to study the structure of a thin film of a phase-separated blend of two conjugated polymers prepared by spin-casting. We show that in addition to the well-known micrometre-scale phase-separated morphology of the blend, one of the polymers preferentially wets the surface and forms a 10-nm-thick, partially crystallized wetting layer. Using near-field microscopy we identify unexpected changes in the fluorescence emission from the blend that occurs in a 300-nm-wide band located at the interface between the different phase-separated domains. Our measurements provide an insight into the complex structure of phase-separated conjugated-polymer thin films. Characterizing and controlling the properties of the interfaces in such films will be critical in the further development of efficient optoelectronic devices.

Accurate Determination of Quantity of Material in Thin Films by Rutherford Backscattering Spectrometry

“…Interestingly, this depended for its sensitivity on the simultaneous detection of the (identical) forward scattered and forward recoiled particles (with a 17 MeV incident proton beam), a basic quantum mechanical problem first considered by Nevill Mott [27]. The structure of thin films involving polymer blends also have many important applications, and the mixing profiles can be systematically followed by deuterating one polymer and profiling the deuterium by 3 He-NRA [28]. Alternatively, a deuterium primary beam can be used to simultaneously profile specific isotopes using NRA, for example 12 PIXE analyses typically use a 3 MeV proton microbeam : elastic backscattering cross-sections are non-Rutherford for 2 MeV protons on all targets of mass up to at least Fe.…”

Local Versus Long‐Range Diffusion Effects of Photoexcited States on Radiative Recombination in Organic–Inorganic Lead Halide Perovskites

“…These two materials were chosen due to their use in photovoltaic cells2, 17, 18, 19 (CH 3 NH 3 PbI 3 ) and light‐emitting diodes8 (CH 3 NH 3 PbBr 3 ). We employ scanning near‐field optical microscopy (SNOM), which has been previously used to study local PL variations in nanostructured systems like polymer thin films,20 inorganic quantum structures,21 and polymer blends 22, 23. Recently, high spatial resolution techniques have been used to study charge extraction in hybrid lead halide perovskite cells and recombination in perovskite nanocrystals 10, 24, 25.…”

Imaging the domain structure of organic semiconductor films

“…By keeping the tip of the probe within one aperture length of the sample, illumination is kept in the near-field and the spot-size and hence the resolution is set by the size of the aperture with resolutions of 50-100 nm routinely achievable. NSOM measurements have been used relatively early on for the characterization of light-emitting conjugated polymers, 17,18 and for probing local photophysics 19,20 and device action, 21 but have only recently been used with polycrystalline thin-film organic transistors in mind. Kuehn et al 22 have recently used NSOM to characterize the domain structure of spin-coated oligomeric PQT-12 films where PQT-12 is the polythiophene poly(3,3 00 -didodecyl-[2,2 0 :5 0 ,2 00 ,2 000 ]-quaterthiophene).…”